The present invention relates to a process for the suspension polymerization of polyurethanes. More particularly, the present suspension polymerization process utilizes silicone surfactants to produce polyurethanes having a very fine particle size which are ideally suited for roto casting or other spin molding operations, fluidized bed coatings, and the like.
Heretofore, polyurethanes have been generally prepared either in bulk or solution. Utilization of either the bulk or a solution polymerization method does not result in fine powders which are often necessary as in the case of molding urethanes through roto casting, fluidized beds, etc. Powders can only be obtained by pelletizing, grinding, and the like at very low temperatures and thus, constitute an expensive process.
U.S. Pat. No. 2,973,333 to Katz discloses the production of polyurethanes by reacting bischloroformates of a diol with a diamine. A very similar U.S. Pat. No. is Katz, 3,089,864, which was divided from the patent application later maturing into U.S. Pat. No. 2,973,333. In yet another Katz Patent, U.S. Pat. No. 2,929,802, polyurethane is made by a similar condensation reaction between monomeric diamines and bischloroformates derived from a low molecular weight glycol. In all of these three patents, the preferred methods for preparing polyurethanes is by a polymerization in an emulsion wherein water constitutes the continuous phase while an inert water-miscible liquid which is solvent for each polymeric reactant as well as a temporary solvent for the formed polymer, constitutes the dispersed phase. Polymerization occurs through an interfacial reaction. Moreover, the organic medium dissolves the formed polymer necessitating the addition of a precipitating solvent. Similarly, U.S. Pat. Nos. 3,485,802 and 3,377,322 to Witsiepe also relate to interfacial polymerization of bishaloformates of esters or ethers with diamines such as piperazine to produce polyurethanes. As with Katz, a precipitating solvent is generally utilized.
Of interest is French Patent No. 1,335,037 which relates to catalytic systems for the production of nonurethane dispersed polymers and British Patent No. 1,007,476, which generally relates to polymerized ethylenically unsaturated monomers which are polymerized to obtain a product in a very finely divided form as suspensions of particles of the polymeric product in an organic medium. Typical polymers are styrene, polyvinyl chloride, acrylonitrile and rubbers such as polybutadiene.
Urea-urethane polymers have been produced utilizing diamines with the aid of some agitation. In U.S. Pat. No. 3,872,049, these solid urea-urethane particles are prepared by utilizing a diamine curing agent and an isocyanate terminated urethane prepolymer of a hydroxy-terminated polyester polyol. The liquid reaction medium contains aromatic hydrocarbon solvents which swell the chain extended urea-urethane polymer. The polymer is then separated by pouring it into an aliphatic or alicyclic hydrocarbon. Generally, very finely divided urea-urethane particles are not obtained and the polymers tend to exhibit high gel. Another prior art patent, U.S. Pat. No. 3,655,627, relates to preparing solid particles of urea-urethane polymers by reacting urethane prepolymers made from diisocyanates and polyols in an aqueous medium with primary diamines. U.S. Pat. No. 3,525,717, also relates to the preparation of urea-urethane polymers by reacting isocyanate-terminated polyesters or polyethers in a water-miscible solvent with a diamine.
U.S. Pat. No. 3,917,741 to McGarr relates to the production of urethane powders. As set forth in this patent, reactive materials which form solid polyurethane resins are introduced into an organic liquid medium which is inert to the reactive materials and in which at least one of the reactive materials and the solid polyurethane is insoluble. Reaction between the reactants takes place at the surface of the insoluble reactive material which is emulsified as fine droplets and thus an interface reaction occurs. Intensive agitation is required along with a specific type of surfactant. Generally the surfactant is an organic copolymer such as a product of copolymerizing vinyl pyrrolidone with an alkylated olefin. A specific example is a copolymer of vinyl pyrrolidone and hexadecene-1.
Yet another prior art patent which relates to the formation of urethane powders or granules is British Patent No. 1,408,945 wherein the urethane prepolymer is dissolved in a chemically inert and anhydrous solvent and chain extended. Then a volatile tertiary amine is added as a catalyst and the reaction proceeds until the initially clear solution gradually passes into a dispersion. The dispersion is then subjected to a steam treatment wherein the polyurethane is separated. Preferred solvents form an azeotropic mixture with water and suitable solvents include xylene and toluene.
In contrast to these prior art patents, the present invention does not utilize aromatic hydrocarbons, water systems, or the like but rather relates to the use of aliphatic hydrocarbon solvents, diol chain extenders and silicone-type suspending agents in a nonaqueous system to produce solely polyurethanes via a two step or a one step process having very fine particle size and which urethane particles are ideally suited for roto casting or spin molding operations, wherein the urethane polymers can be cured utilizing specific curing agents. Additionally, any urethane suspension polymers having a plasticity of 2,000 square mm. or more at 150.degree. C, can be cured during a spin molding operation when specific curing agents are used.